Guardian 4389 Repair Manual page 74

SECTION 4.1
DESCRIPTION AND COMPONENTS
GENERAL
This section will familiarize the reader with the various
components that make up the DC control system.
Major DC control system components that will be cov-
ered include the following:
• A Terminal Strip / Interconnection Terminal
• A Transformer (TX)
• A Circuit Board.
• An AUTO-OFF-MANUAL Switch.
• A 15 Amp Fuse.
• A 5 Amp Fuse.
TERMINAL STRIP / INTERCONNECTION
TERMINAL
The terminals of this terminal strip are connected to
identically numbered terminals on a prepackaged
transfer switch terminal board. The terminal board
connects the transfer switch to the circuit board and
transformer.
The terminal board provides the following connection
points:
A. UTILITY 1 and UTILITY 2
1. Connect to identically marked terminals on a
prepackaged transfer switch terminal board.
2. The circuit delivers "Utility" power source volt-
age to the transformer (TX) located in the con-
trol panel assembly.
B. 23 and 194
1. Connect to identically numbered terminals on
the terminal board of the prepackaged transfer
switch.
2. This circuit connects the circuit board to the
transfer relay coil in the prepackaged transfer
switch.
Figure 1. Terminal Board
TRANSFORMER (TX)
The control panel assembly's transformer is a step-
down type. The line-to-line voltage from the UTILITY
1/UTILITY 2 terminals is delivered to the trans-
former's primary winding. Transformer action then
induces a reduced voltage (about 12 to 16 volts) into
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PART 4
both secondary transformer windings. Reduced volt-
age from one secondary winding is delivered to the
circuit board as "Utility" source sensing voltage.
Reduced voltage from the other secondary winding is
delivered to the battery charger for trickle charging.
• If the Utility sensing voltage drops below a preset
value, circuit board action will initiate automatic
generator startup and transfer to the "Standby"
source side.
The sensing transformer is shown in Figure 2, both
pictorially and schematically.
1
230V
50/60Hz
5
Figure 2. The Transformer
CIRCUIT BOARD
The circuit board controls all standby electric system
operations including (a) engine startup, (b) engine
running, (c) automatic transfer, (d) automatic retrans-
fer, and (e) engine shutdown. In addition, the circuit
board performs the following functions:
• Delivers "field boost" current to the generator rotor
windings (see "Field Boost Circuit" in Section 2.2).
• Starts and "exercises" the generator once every
seven days.
• Provides automatic engine shutdown in the event of
low oil pressure, high oil temperature, or over-
speed.
A 17-pin and a 5-pin connector are used to intercon-
nect the circuit board with the various circuits of the
DC systems. Connector pin numbers, associated
wires and circuit functions are listed in the CHART on
the next page.
The circuit board mounts a crank relay (K1) and a run
relay (K2, see Figure 3). Crank relay (K1) is ener-
gized by circuit board action during both manual and
automatic startup to crank the engine. Cranking is
accomplished in crank-rest cycles, with the first cycle
being 15 seconds on and 15 seconds off. After the
first crank-rest cycle, the remaining cycles will be in
equal 7-9 second durations. This cyclic cranking
action continues until either (a) the engine starts, or
(b) approximately 90 seconds of the crank-rest cycles
have elapsed.
DC CONTROL
6
16V
56VA
7
9
16V
1VA
10
SCHEMATIC